Variable stroke cylinder

ABSTRACT

In a variable stroke cylinder having a pair of pistons in which the distance between the pistons is selectively variable for selectively varying the stroke of the cylinder, a vent communicates with the space between the pistons for venting the space when the distance between the pistons is being varied.

O I Umted States Patent 11 1 1111 3,815,480 Spyra June 11, 1974 [54]VARIABLE STROKE CYLINDER 2,556,979 6/1951 Purcell 92/257 )4 2,703,557 3l955 P lk' 92 l3.5| X [76] Inventor: Rudolf A Spyra, 5344 N. Paulma2946'3'8 72960 Rzthlerford U -1 Chicago, 60640 2,977,167 3/1961 Bamhart92/82 1 Filed= 17, 1969 FOREIGN PATENTS OR APPLICATIONS [211 Appl. No.:877,257 1,119,789 12/1961 Germany 92/13 Prima Examiner-Irwin C. Cohen 5..9l. 91.8,9 77 I 2] U S Cl 2/ 3 2/ 3 2/1 Attorney, Agent, orFzrm-Molmare, Allegrettl, Newltt [51] Int. Cl. F0lb 31/00 & ff [58]Field of Search 92/13, 13.51, 13.8, 255,

[57] ABSTRACT [56] References C'ted In a variable stroke cylinder havinga pair of pistons in UNITED STATES PATENTS which the distance betweenthe pistons is selectively 108,426 10/1870 Young I. 92/257 Xvariable-for selectively varying the stroke of the cylin- 1,325,00612/1919 Dearsley 92/1351 der, a vent communicates with the space betweenthe 2,196,224 4/1 40 Morgan 13451 pistons for venting the space when thedistance be- 2,42s,493 10/1947 Haller 92/l3.8 tween the pistons is beingmay 2,465,600 3/1949 Munk 92/l3.8 X 2,478,790 8/1949 Stephens 92/13.6 X5 Claims, 3 Drawing Figures ns /8 0./ I34 20- g;

27'- l as 38 MTENTEDJUH 1 1 m4 Wall/1141412.

INVENTOR.

RUDOLF ,4. SPYRA ATTORNEYS I VARIABLE STROKE CYLINDER BACKGROUND ANDSUMMARY OF THE INVENTION This invention relates to a variable strokecylinder and. more particularly, to a double piston cylinder in whichthe distance between the pistons may be easily and readily varied tovary the stroke of the cylinder.

It is frequently desirable that a given pneumatic or hydraulic motor orpumping cylinder be capable of varied input and/or output depending uponconditions encountered during use in a given system. One manner whichhas been employed in the past to so vary the input and/or output of suchcylinders, has been to selectively increase or decrease the stroke ofthe power member or piston of the cylinder.

Various methods have been employed in the past to vary or adjust thestroke for this purpose. One manner of effecting such variation, hasbeen by the use of electrical switching devices. Mechanical methods havealso been employed. In the mechanical method, rather than a singleworking piston, a pair of working pistons are provided in the cylinderand the distance between the pistons may be selectively varied to varythe'stroke of the cylinder. When the pistons are moved toward eachother, the stroke will be increased and when the pistons are moved awayfrom each other the stroke will decrease. By way of example, a doublepiston variable stroke cylinder is shown in United States Letters PatentNo. 1,325,006.

As shown in said patent, the pistons are fitted within the cylinder witha close tolerance between the outer perimeter of each of the pistons andthe cylinder wall so as to effect a sealing engagement between the pis-'tons and the cylinder wall. As a result of this sealing engagement,variable adjustment either of one of the pistons relative to the otheror. of both pistons simultaneously is rendered diff cult, if notimpossible under some circumstances, due to the compression or expansionof the fluid sealed between the pistons. For example, when the pistonsare adjusted apart so as to decrease the cylinder stroke, aprogressively increasing vacuum condition occurs in the space betweenthe pistons asadjustment'proceeds. This vacuum conditionrendersladjustment progressively more difficultand adjustment may evenbecome impossible where the stroke is to be widely varied. Conversely,when the pistons are moved closer together so as to increase the stroke,a pressure condition arises between the pistons which also progressivelyincreases as adjustment proceeds. Particularly in the latter situationand where the cylinder is for hydraulic use, any leakage which may occurbetween the pistons and the cylinder wall into the space between thepistons during prolonged minimum stroke operation, may render adjustmentto the maximum stroke condition impossible due to the noncompressiblenature of the hydraulic liquid.

The variable stroke cylinder of my invention overcomes thesedisadvantages. In the variable stroke cylinder incorporating theprinciples of my invention, a double piston cylinder is provided inwhich the stroke is capable of being readily and easily mechanicallyvaried over a wide range. In the cylinder of my invention, the effortnecessary to adjust the stroke is both minimal and uniform over theentire range of adjustment since the likelihood of vacuum or pressureconditions occurring in the space between the pistons is obviated.Moreover, in the cylinder incorporating the principles of my invention,the stroke may be readily adjustedvfrom the exterior of the cylinder,without necessitating disassembly of same and, once adjustment has beenmade, the pistons may be locked relative to each other to insurereliable operation over continued periods at the adjusted stroke in oneof the embodiments of my invention.

In a principal aspect, the variable stroke cylinder incorporating theprinciples of my invention includes a pair of piston members positionedin a cylinder and at least one of said piston members is selectivelymoveable relative to the other for adjustably varying the stroke of thepiston members. In my invention, vent means is provided whichcommunicates with the space between the piston members so as to vent thespace when the distance between the piston members is varied to vary thestroke of the cylinder.

In another aspect, locking means is provided whereby once the stroke hasbeen adjusted, the piston members may be locked relative to each other.

In another aspect, each of the pistons, as well as the cylinder, are ofnon-curvilinear cross section, whereby when one of the piston rods isrotated relative to its piston, stroke variation is effected.

These and other objects, features and advantages of the presentinvention will be more clearly understood through a consideration of thefollowing detailed description.

BRIEF DESCRIPTION or THE DRAWING In the. course of this description,reference will frequently be made to the attached drawing in which:

FIG. 1 is an elevation cross sectioned view'of one preferred embodimentof variable stroke cylinder constructed in accordance with theprinciples of my invention;

FIG. 2 is a partially cut away elevation cross sectioned view of asecond preferred embodiment of variable stroke cylinder constructed inaccordance with the principles of my invention; and

FIG. 3 is a partially cut away perspective view of a third preferredembodiment of variable stroke cylinder constructed in accordance withthe principles of my invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, onepreferred embodiment of variable stroke cylinder of my invention isshown. The cylinder comprises an elongated cylinder sleeve 10 closed ateach end by cylinder heads 11 and 12 which may be threadedlysecured toeach end of the cylinder sleeve by way of threads 14. A suitable sealinggasket, such as an O-ring 16, may be carried in a groove 18 adjacent theinner end of each of the heads 11 and 12 so as to sealingly contact theinner wall 20 of the sleeve.

a diameter such that when the rod 24 is journalled through the passage,an annular space obtains between the head 21 and exterior of the rodwhich has a cross section substantially equal to the cross sectionalarea of passage 22 to provide for a uniform suction and discharge ratethrough-each of the passages. A suitable sealing gland 25 is fitted inthe top of passage 21 and engages the piston rod 24 to seal the passage,but provide for sliding movement of the rod.

A pair of pistons 26 and 27 are positioned within the cylinder sleeve,10 and divide the interior of the sleeve into a pair of workingchambers 28 and 29. Piston 26 is firmly threaded at 30 onto one end ofpiston rod 24 and theotherpiston 27 is also threaded at 32 on one end ofanother piston rod 34 and stationarily locked thereto by nut 36 which isreceived in a recess 38 in piston 27. Rod 24 is annular in cross sectionand rod 34 extends upward therethrough in journalled relationship. Theend of rod 34 opposite its piston is externally threaded at 40 and rod24 is internally threaded so that rods 24 and 34 may be axiallythreadedly adjusted relative to eachother between the position shown insolid in FIG. 1 'andthe dot and dash line position also shown therein.Adrive fitting may be carried on the end; of either of the rods similarto the fitting D shown in FIG.

A seal ring 42, formed of suitable sealing material, is carried in agroove 44 about the inner periphery-of rod 24 adjacent its piston andsealinglyengages the external surface of rod 34 to seal off the space 46bet-ween thepistons 26 and 27 from the small annular area between rod 34and the interior wall of rod Suitable piston sealing rings 47 and 48are'also carried in annular grooves 49 and 50 about each of. the pistons26 and 27, respectively, and are arranged to slidingly and sealingly'engage the internal wall 20 of the cylinder sleeve to prevent: leakagebetween the pistons and'wall.

.' An important feature of my invention is the provision ofmeans toequalize the-pressure between space'28 and thespace=46 between thepistons during adjustment of the piston stroke. As shown in FIG. 1, thismeans comprises ableed orifice S2which extends between the faces ofandthrough the thickness of piston: "'26 andcommunicates space 46 withthe working space 28 above the piston. Bleed orifice 52 is oil-a sizesuch that little fluid transfer will occur between space 28 and space46during normaloperation of the cylinder either as a pump or as a motor.However, when it is desired to either increase or decrease the stroke ofthe cylinder, thebleed orifice operates to vent the space 46 and enableeasy and uniform adjustment of thecylinder stroke.

4 to be decreased, rod 24 is rotated in the opposite direction movingpiston 26 closer to piston 27. Again relatively constant pressureconditions will obtain in space 46 during such adjustment, since anypressure buildup will be vented from space 46 to space 28 by way to thebleed orifice. I

Referring to FIG. 2, another embodiment of variable stroke cylinder ofmy invention is shown in which looking means is provided to lock thepiston heads relative to each other once stroke adjustment has beencompleted. Like the embodiment shown in FIG. 1, a pair of pistons 56 and57 are positioned within cylinder sleeve 10. A tubular piston rod 58,somewhat similar to rod 24 in FIG. I, is fixed by way of threaded end 60and nut 61 to piston 56 and extends through one head of the cylinder(not shown) in a manner similar to that shown in head 11 in FIG. 1. Asecond rod 62 extends through the other head (not shown) of thecylinder. The distal end of piston rod 62 is of reduced diameter andexternally threaded at 64 over its reduced diameter length. Piston rod62 is threaded through piston 57 and locked thereto by a locknut 66'andthe remaining threaded portion is threadedly received in the tubular rod58 which is also internally threaded at 68 over its length. A threadedplug 70 is threaded into therod 58 from the other end and intocontactwith the distal end of the piston rod 62 so as to lock the rod 62 atwhatever depth it has been threaded. The plug 70, includes a suitabletool receiving surface 72 at its outer end to allow for tighteningandloosening-of the plug.

In order to adjust the stroke of the cylinder shown in FIG. 2, plug 70is rotated so as to moveupward and out contact with the distal end ofthe piston rod 62, locking I the pistons in their adjusted spacedrelationship.

The venting arrangementshown in FIG. 2 is somewhat different than thatpreviously described. Instead of providing a bleed orifice throughpiston 56, the seal rings 47 have'been eliminated and the diameter ofpiston 56 is reduced slightly so as to provide for a small solidposition to the dot and dash position shown in FIG. 1, piston 26 willmove relatively away from the piston27. Since the volume of the space 46between the piston will increase, vacuum conditions would normallyoccurtherein due to the tight seal provided by sealing rings 47 and 48and continued adjustment would become progressively more difficult.However, due to the orifice 52, a relatively constant pressure will bemaintained at all times in space 46 due to the venting of fluid fromspace 28 to space 46. If the storke is annular clearance space 74between the perimeter of piston 56 and the inner wall 20 of the cylindersleeve. Thus, during adjustment fluid will vent to or from spaces 46 and28 through the annular clearance space.

Another embodiment of variable stroke cylinder of my invention is shownin FIG. 3. In this embodiment, a rod 76 threadedover its length, isthreaded through piston 56' and loc'knuts 77 and 78 are threaded ontoone end of rod 76 into firm contact with the opposite faces of thepiston so as to fix rod 76 to the piston. Rod 76 extends downwardthrough piston 57' and is threaded into a tubular rod 80 which carries adrive fitting D at its other end. The tubular rod 80 is mounted topiston 57' for rotation relative thereto by way of a shoulder 82 at oneside of the piston and a washer and nut 84 which is spaced slightlyabove the upper face of the piston 57 and in contact with a slightlyraised shoulder 85 adjacent the end of rod 80. A slot 86 extends over aportion of the length of the rod 76 and a key-like insert 88, threadedto match the threads on rod 76, is received therein. The threads of theinsert 88 are substantially flush with the threads on rod 76. The insert88 is formed of nylon or other non-metallic material and provides atight fit and a pre-load effect between rods 76 and 80.

To adjust the stroke of the cylinder shown in FIG. 3, tubular rod 80 isrotated. Since rod 76 is fixed to piston 56 and also since the pistons56 and 57' are prevented from rotating due to their rectangular crosssection, rod 76 will move axially into or out of rod 80 driving piston56' toward or away from piston 57 to effect stroke adjustment.

Since tubular rod 80 is also rotatable relative to its piston 57, one ormore seal rings 90 are preferably positioned in the piston for sealinglybearing against the external surface of the rod to prevent leakagebetween chambers 20 and 46 during operation of the cylinder. Again toinsure venting of the space 46 between the pistons during adjustment,annular space 74 may be provided about piston 56 or a ventingarrangement similar to that shown in FIG. 1 may be provided.

It will be appreciated that although my invention has been described asemployed in a duplex cylinder, it may also be employed in a cylinder-ofsimplex design by merely positioning both passages 21 and 22 at one endof the cylinder and providing a sealed pneumatic cushion space at theother end thereof. Moreover, it will also be understood that theembodiments of the present invention which have been described aremerely illustrative of some of the applications of the principles of theinvention. Numerous modifications may be made by those skilled in theart without departing from the true spirit and scope of the invention.

What is claimed is:

, 1. In a variable stroke cylinder, a cylinder member, a pair of pistonmembers spaced a predetermined distance from each other so as to definea space therebetween, said piston members being mounted for simultaneousaxial movement in said cylinder member during normal operation thereof,means for selectively moving at least one of said piston membersrelative to the other said piston member for adjustably varying thestroke of said piston members by moving said piston members relative toeach other to vary said predetermined distance between said members, theimprovement which enables rapid and extensive stroke adjustment thereinand which comprises in combination therewith:

vent means communicating with said space between said piston members forventing said space when said predetermined distance between the pistonmembers is varied to vary the stroke of the cylinder to maintain thepressure in said space substantially constant during said strokeadjustment, wherein said vent means comprises a bleed orifice in one ofsaid piston members communicating between the face of said piston memberadjacent said space and the opposite face of said piston member.

2. The cylinder of claim I wherein said bleed orifice is in saidselectively moveable piston member.

3. The cylinder of claim 1 wherein said piston members include anelongated rod, the rod of one of said piston members being threadedlyjournaled through the other of said rods, whereby rotation of one ofsaid rod effects said selective relative movement of said pistonmembers.

4. The cylinder of claim 3 further including locking means, comprisingthreaded plug means positioned in the second mentioned rod and movableinto contact with the first mentioned rod.

5. The cylinder of claim 3 wherein said piston members and said cylindermember are non-circular in cross section for preventing rotation of saidpiston members, and at least one of said rods is rotatable relative toits piston member to effect said selective relative movement of saidpiston members.

1. In a variable stroke cylinder, a cylinder member, a pair of pistonmembers spaced a predetermined distance from each other so as to definea space therebetween, said piston members being mounted for simultaneousaxial movement in said cylinder member during normal operation thereof,means for selectively moving at least one of said piston membersrelative to the other said piston member for adjustably varying thestroke of said piston members by moving said piston members relative toeach other to vary said predetermined distance between said members, theimprovement which enables rapid and extensive stroke adjustment thereinand which comprises in combination therewith: vent means communicatingwith said space between said piston members for venting said space whensaid predetermined distance between the piston members is varied to varythe stroke of the cylinder to maintain the pressure in said spacesubstantially constant during said stroke adjustment, wherein said ventmeans comprises a bleed orifice in one of said piston memberscommunicating between the face of said piston member adjacent said spaceand the opposite face of said piston member.
 2. The cylinder of claim 1wherein said bleed orifice is in said selectively moveable pistonmember.
 3. The cylinder of claim 1 wherein said piston members includean elongated rod, the rod of one of said piston members being threadedlyjournaled through the other of said rods, whereby rotation of one ofsaid rod effects said selective relative movement of said pistonmembers.
 4. The cylinder of claim 3 further including locking means,comprising threaded plug means positioned in the second mentioned rodand movable into contact with the first mentioned rod.
 5. The cylinderof claim 3 wherein said piston members and said cylinder member arenon-circular in cross section for preventing rotation of said pistonmembers, and at least one of said rods is rotatable relative to itspiston member to effect said selective relative movement of said pistonmembers.